Canaries Sometimes Sing (1930)

Geoffrey and his wife Anne are trapped in a stifling marriage, which neither feels able to leave. When Geoffrey's boyhood friend, Ernest, and his new wife, Elma, come for a long visit, it's soon apparent that their marriage is equally unhappy. As Ernest and Anne strike up a supposedly secret affair, Geoffrey and Elma do everything they can to encourage their spouses' infidelity, whilst also pretending to be blissfully unaware of it.